Thursday, January 15, 2015

The Eel's in Charge

By: Paul Carvalho

Before Jack Cover of NASA
developed the Taser stun gun, evolution and natural selection whipped up these bad
boys.

The electric eel (Electrophorus
electricus) is capable
of discharging electricity for navigation, defense, and attack purposes. They shock their prey into a stupor until the
helpless fish twitches uncontrollably. Once the eel feels a slight movement in
the water from the twitch, they attack and the fish is a goner. Recently, researchers
at Vanderbilt University in Nashville, Tennessee have discovered that eels can also
use their shocking ability to remotely control prey items.

Electric eels (endemic to
South America), and many other electrogenic fish in the order Gymnotiformes
have evolved an insane cell known as the electrocyte. They are derived from
muscle cells and have lost the ability to contract, however, these cells have
developed into natural batteries within the eels. Most electrogenic fish have one electric organ
made up of these cells, but this gangster fish contains THREE electric organs (Sachs, Main, and Hunter’s) running along the
whole body. All three add up to 6,000 electrocytes allowing this beast to
generate 600 volts- that is five times that of a U.S. wall outlet!

Electric eels have three
forms of emitting electricity from their organs. The first is used for
navigation and consists of low-voltage pulses.
The second is a high-voltage pulse, released in pairs or triplets for
hunting, typically used in a complex environment with a lot of hiding places
for tasty snacks. The third is a series of high-voltage pulses used for freezing
free-swimming prey animals in their tracks. The third form can also be used as
a defense mechanism against haters, like the caiman featured in the video below.

Be aware of the creepy
clown laugh in the beginning and end of this video!

Although these forms of
electrical discharge have been known for quite some time, little was known
about the impact of the discharge on prey. Kenneth Catania from Vanderbilt
University designed an experiment to explore how the electrical charge affects
prey during an attack. To examine the effects of high-voltage discharge on prey,
Catania set up a tank with a gel barrier permeable to electrical current. A scramble-brained
fish fixed to a device that measured muscle tension was lowered into one side
of the tank with a hungry eel on the other side. Worms were dropped into the
eel’s side of the tank in order to initiate an attack response. The fish’s muscles
contracted during this test, indicating that the muscles of the prey are FORCED to contract during an attack (A
and B in the following figure).

Catania suspected that muscle contractions in the
fish may be directly caused by the electrical charge stimulating muscle cells or
by stimulating motor neurons in the prey. To explore these options,
two fish were placed side by side in the gel-divided tank. One fish was
injected with an acetylcholine antagonist (basically a shot disrupting the interaction
between the motor neurons and muscle cells) and the other fish was injected
with a control. The results seen in the above figure (C and D), show that the tension
in the acetylcholine antagonist-treated fish declines to nothing after
injection. This reveals that fish motor neuron activity is necessary for the eel’s
electrical discharge to affect muscle contraction in prey.

Now let’s talk about that
second form of electrical discharge mentioned above. Eels will sometimes use
high-voltage pulses in doublets or triplets while hunting. Catania noticed that
eels would release an isolated doublet and wait for prey to tweak out. Once the
eel detected the prey’s movement in the water, the eel releases the attack
response, much like we were just talking about. This attack stuns the prey so
it can move in for the kill. To test his theory, Catania put a fish in a
plastic bag inside some gel and hooked it up to a machine that the experimenter
can use to stimulate a twitch in the fish. The fish was also protected from the
electrical doublet sent out from the eel, so unless the researcher induces the
twitch, the eel has no clue anything is there.

When the eel released its
doublet, the researcher stimulated the fish to twitch. In response, the eel
used a high voltage pulse and tried to attack the fish. This happened every
time the experimenter simulated a twitch in the fish. When a doublet was
released and the researcher did not simulate a twitch, the eels did not gear
into attack mode- it was just business as usual.

Now this is truly amazing!
At least I think so. These eels can swim around cracks and holes and not detect
a prey item but with this “doublet hunting” method they can remotely control
the muscle contraction of some poor unfortunate soul giving away their position
and leading to their demise.

Now if you ever go to
South America looking for some electric eels, learn a thing or two from the
following video before you embark on that journey.